. >> on thursday, the white house said it had concluded with some confidence that the syrian government had used chemical weapons. the british government is backing that as well. obama added on friday again that chemical weapons use is a game changer. >> the claims have not changed anything on the ground in syria. government troops pushed into two northern damascus neighborhoods on friday, triggering heavy fighting with rebels. >> syrian government forces are concentrating their firepower on damascus. troops loyal to the regime have been pounding rebel positions. as the fighting escalates, so does evidence that the regime has used a deadly chemical agents against rebel forces. has the syrian president crossed the red line? that would be a game changer for western nations. the u.s. president, barack obama, said investigations were still ongoing, but -- >> the use of potential weapons of mass destruction on civilian populations crosses another line with respect to international norms and international law. that is going to be a game changer. >> british prime minister david cameron emphasi